TS-113
Experimental Characterization of the EHL Film Thickness of Traction Lubricant
K.Iwamoto*, P.Ehret**
ABSTRACT
A large number of marine mechanical elements critically relies upon the successful running conditions of a wide range of components such as gears, cams or rolling bearing elements. In such components, the lubrication regime is commonly referred to as elastohydrodynamic lubrication (EHL) regime. The load is transferred over a small contact area generating high pressure within lubricant film which separates the bounding surfaces. As a result important deformation of the surface occurs locally which is important to take into consideration during the design of the element. In this study, the minimum lubricant film thickness and central film thickness were measured using an optical interferometry method. Interferometry method was used to measure the film thickness in a lubricated contact between a transparent glass disc and a reflective steel ball. Ball and disc was driven independently to allow any slide/roll ratio. The optical system used to measure film thickness was composed of a microscope, a high resolution colour video camera and a high intensity white light source. To complement the film thickness measurement, the apparatus also enables the traction force on the surface of the disc to be obtained. Using this apparatus the EHL performance of two traction lubricants was analysed and compared.
Key Words; EHL, Traction Lubricant, Characterization, Film Thickness
1. INTRODUCTION
EHL has been studied both theoretically and experimentally for many years. Cameron & Gohar [1] measured film thickness under the condition of EHL point contact by using interferometry method and obtained an approximate solutions which were based upon the Grubin approach established for line contact. Hamrock and Dowson [2] presented an expression which give numerical solution within a wide range condition for EHL point contact. The result of the central and minimum oil film thickness, which are obtained by the expression, were coincide with experimental results. The expressions have been widely used in the design and analysis of machine elements. In recent years, tribological machine components as traction drive require lower power loss and higher efficiency of machines in EHL conjunctions. Therefore, it is important to look at the performance of these components. Oil film thickness is important value which indicate a condition of lubrication because in a case of smaller oil film thickness, much wear or injury generates in mechanical elements. Oil film thickness are obtained by speed, material and load parameters in the expression. Speed and load parameter are determined by running condition and material parameter is determined by characteristics of lubricants.
In this study, the minimum oil film thickness and central film thickness were measured using an optical interferometry method. The EHL performance of two traction lubricants was analysed and compared with experimental results. Pressure viscosity coefficients of traction lubricants were obtained from some experiments.
2. EXPERIMENT
Fig.1 shows the experimental apparatus which consist of the ball and disc system. This system is used very often as a apparatus for study of EHL because in this system, it is easy to measure the oil film thickness. Interferometry method was used to measure the film thickness in a lubricated contact between a transparent glass disc and a reflective steel ball.
* Tokyo University of Mercantile Marine
2-1-6 Etchujima, Koto-ku, Tokyo 135-8533 JAPAN
FAX: +81-3-5245-7433, E-mail: iwamoto@ipc.tosho-u.ac.jp
** University of Leeds
